Phosphorylation of the RNA polymerase II CTD (C-terminal repeat domain) occurs at a critical decision point in gene expression, beginning active transcription elongation. To investigate this modification of PoI Il, we previously purified a novel CTD kinase, yeast CTDK-I, and showed that this enzyme is essential for normal cell growth and CTD phosphorylation. Our current objectives are to characterize in detail the in vivo and in vitro properties of CTDK-I and to learn more about meanings and mechanisms of CTD phosphorylation. Toward these ends we plan experiments to: * investigate the specific role(s) of CTDK-I in pre-mRNA synthesis in vivo; we will exploit strains containing mutations affecting CTDK-I. * identify processes and components influencing or influenced by CTD phosphorylation; we will select and characterize alleles of other genes that suppress growth defects of CTDK-I mutants. * investigate and define the role of CTDK-I in transcription in vitro: we will use a biochemical complementation approach and extracts from mutant and wild type strains. * characterize in detail enzymological properties of CTDK-I. * investigate in vivo behavior of differently phosphorylated Pol II forms and of general transcription factors associated with Pol II. Defects in regulation of transcription initiation or elongation can lead to abnormal cell growth and cancer. Steps in the transcription process involved with or influenced by CTD phosphorylation are candidates for defective regulation that might cause aberrant growth and disease. Therefore a thorough characterization of CTD kinases like CTDK-I is important for elucidating gene expression mechanisms, for understanding malfunctions of those mechanisms in disease states, and for designing rational defenses against or cures for such malfunctions.